Ammunition and the firearm that the ammunition is used in have to function together. In order to facilitate this, dimensions of ammunition and the firearm chambers that it has to function in are very tightly dimensionally controlled. A variety of organizations exist that provide standards in order to help assure smooth functioning of all ammunition in all weapons. Non-limiting examples of these organizations include the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) in USA, the Commission Internationale Permanente pour l'épreuve des armes à feu portatives (CIP) in Europe, as well as various militaries around the globe ans transnational organizations such as the North Atlantic Treaty Organization (NATO).
SAAMI is the preeminent North American organization maintaining and publishing standards for dimensions of ammunition and firearms. Typically, SAAMI and other regulating agencies will publish two drawings, one that shows the minimum (MIN) dimensions for the chamber (i.e. dimensions that the chamber cannot be smaller than), and one that shows the maximum (MAX) ammunition external dimensions (i.e. dimensions that the ammunition cannot exceed). The MIN chamber dimension is always larger than the MAX ammunition dimension, assuring that the ammunition round will fit inside the weapon chamber. All published SAAMI, NATO, US Department of Defense (US DOD) and CIP drawings are incorporated here by reference.
It is important to note that SAAMI compliance and standardization is voluntary. SAAMI does not regulate all possible calibers, especially those for which the primary use is military (for example, .50 BMG (12.7 mm) calibers are maintained by the US DOD), or the calibers which have not yet been submitted (wildcat rounds, obscure calibers, etc.)
In general, new cases developed for established calibers (for which chamber/ammunition drawings are published) have to follow the published external dimensions very closely in order to function in the maximum number of weapons. This has also been true for development of cases with alternative case materials, such as for example polymers (see, e.g., U.S. Pat. Nos. 8,240,252 and 8,813,650, each of which are incorporated herein by reference). Polymer cases have been an active area of research for a number of years as they offer advantages in areas such as ammunition weight and accuracy. The current invention provides ammunition casings having dimensional profiles optimized for polymeric ammunition.